Date of Graduation

5-2018

Document Type

Thesis

Degree Name

Master of Science in Food Science (MS)

Degree Level

Graduate

Department

Food Science

Advisor

Trenton Roberts

Committee Member

Yeshi Wamishe

Second Committee Member

Jarrod Hardke

Third Committee Member

David Miller

Keywords

Agriculture, Autumn Decline, Hydrogen Sulfide, Rice, Soil

Abstract

Rice (Oryza sativa L.) producers face many challenges throughout each growing season. Hydrogen sulfide (H2S) toxicity is a physiological disorder where sulfate (SO42-) is excessively reduced to the toxic gas, H2S. This can reduce yield and, in severe cases, result in crop death. The main research objectives were to: i) understand chemical and physical characteristics in soils prone to H2S toxicity, ii) determine influential soil characteristics on the incidence of H2S toxicity, iii) determine ammonium sulfate ((NH4)2SO4) fertilizer additions influence on H2S toxicity, and iv) predict when and where H2S will occur. Three greenhouse experiments were conducted using Arkansas field soils with varying degrees of H2S toxicity history. Half of the soils were sterilized in the first experiment, cultivar CL151 planted in the last two experiments, (NH4)2SO4 treatments added to the last experiment, and soil solution samples and redox potential (Eh) monitored in all experiments. Soluble SO42- concentrations were greater (p=0.0231 to 0.0005) and Eh declined slower in sterilized soils, indicating microorganisms important role in reduction. Significant differences in soluble SO42- concentrations between locations on day 21 (p = 0.0310) occurred, however the most and least prone soils were not statistically different, indicating this measure may not be the best indicator for H2S toxicity. A significant interaction between sterilization and location reaffirmed this and the influence of microbes. As rice grew, differences between locations (p = 0.0183 to <0.0001) and fertilizer treatments (p = 0.0275 to < 0.0001) occurred, and SO42- concentrations in the most and least prone soils were different (p = 0.0405 to 0.0106), indicating multiple influential factors. Highest soluble SO42- concentration occurred in a soil not prone to H2S toxicity, indicating that the cause of H2S toxicity is independent of SO42- concentrations. Concentration of SO42- followed fertilizer rate, yet H2S toxicity symptoms did not occur. Though results from these studies did not determine the cause of H2S toxicity, evidence of multiple influential factors was apparent. Further work focused on the interaction of soil microbes and the quantity of terminal electron acceptors in the soil may shed light on the variable severity of H2S toxicity across soils.

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